Heterogeneous photochemistry in ice phases

Gaseous components of molecular clouds tend to condensate on the surface of solid dust particles at low temperatures. These dust particles are produced in the atmospheres of cool giant stars by condensation of refractory materials such as olivine and other silicates, whereas condensation of supernova ejecta results in metallic particles. 

Refractory dust particles not only serve as condensation nuclei for ices (see above), but are also necessary for energy dissipation during gas phase reaction between energetic atoms and molecules. Furthermore, solid inorganic particles (mostly oxides and sulphides) may play a role of photocatalysts in transformations of organic materials in both space and the primitive soup [5, 31]. 

The ice mantles formed on the surface of dust particles can be divided into two main categories according to the chemical composition, which in turn result from 

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The primary photochemical steps should include dissociation of various hydrogen compounds with formation of hydrogen atoms and the following radicals OH, 

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